Fuel injection device for an internal combustion engine

ABSTRACT

The fuel injection system has a high-pressure pump that delivers fuel to an accumulator and fuel supply pump delivers fuel to the suction side of the high-pressure pump, with a fuel metering unit between the fuel supply and high-pressure pumps to variably adjust the fuel quantity taken in by the high-pressure pump. The accumulator is connected to at least one fuel injector and a return leads from the fuel injector(s). The fuel return from the injector(s) feeds into the connection between the fuel supply pump and the fuel metering unit. A connection controlled by a pressure valve leads from the fuel return to a discharge region. The high-pressure pump only draws fuel from the fuel return in operating states in which the fuel quantity delivered by the fuel supply pump is less than the required intake quantity of the high-pressure pump.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a 35 USC 371 application of PCT/DE 2004/001690 filedon Jul. 28, 2004.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The invention is directed to an improved fuel injection system for aninternal combustion engine.

2. Description of the Prior Art

A fuel injection system of the type with which this invention iscornered, known from DE 100 02 132 A1, has a high-pressure pump thatdelivers fuel to an accumulator. A fuel supply pump delivers fuel from afuel tank to the suction side of the high-pressure pump, and a fuelmetering unit between the fuel supply pump and the high-pressure pumpcan variably adjust the quantity of fuel taken in by the high-pressurepump. The accumulator is connected to at least one injector that injectsfuel into the internal combustion engine. A fuel return leads from theinjector back to the fuel tank. In order to assure that thehigh-pressure pump delivers a sufficient supply of fuel to theaccumulator in all operating states of the engine, the fuel supply pumpmust deliver a sufficiently large quantity of fuel to the high-pressurepump. But in order to achieve this, it becomes necessary to provide afuel supply pump with very large dimensions, which increases the weightand amount of space required of the fuel injection system and alsocontributes to high manufacturing costs.

SUMMARY AND ADVANTAGES OF THE INVENTION

The fuel injection system according to the present invention has theadvantage over the prior art that the fuel supply pump can be ofrelatively small dimensions, which makes it possible to minimize thespace required, weight, and costs of the fuel injection system. Onlywhen the quantity of fuel delivered by the fuel supply pump is less thanthe required intake quantity of the high-pressure pump does thehigh-pressure pump also take in additional fuel from the fuel return.This assures that the high-pressure pump takes in predominantly the coolfuel delivered by the fuel supply pump and only the shortfall is made upby the heated fuel from the fuel return.

Advantageous embodiments and modifications of the fuel injection systemaccording to the present invention are disclosed. One embodiment assuresthat the high-pressure pump will only take in fuel from the fuel returnif the fuel quantity delivered by the fuel supply pump falls short ofthe required intake quantity. Another embodiment provides for alubrication and cooling of the drive region of the high-pressure pumpwhile still another assures that the drive region of the high-pressurepump is supplied exclusively with fuel delivered by the fuel supplypump, i.e. cooler fuel. In a further embodiment only the fuel quantitytaken in by the high-pressure pump passes through the filter, thusallowing a smaller or simpler filter design to be used.

BRIEF DESCRIPTION OF THE DRAWINGS

A number of exemplary embodiments of the present invention are explainedin greater detail in the subsequent description, taken in conjunctionwith the drawings, in which:

FIG. 1 is a schematic depiction of a first exemplary embodiment of afuel injection system for an internal combustion engine according to theinvention,

FIG. 2 shows the fuel injection system according to a second exemplaryembodiment, and

FIG. 3 shows the fuel injection system according to a third exemplaryembodiment.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIGS. 1 to 3 show a fuel injection system for an internal combustionengine, for example of a motor vehicle. The engine is an autoignitioninternal combustion engine, for example, and has one or more cylinders.The motor vehicle has a fuel tank 10 that stores fuel for the operationof the engine. The fuel injection system has a fuel supply pump 12 thatdelivers fuel from the fuel tank 10 to a high-pressure pump 14. Thehigh-pressure pump 14 delivers fuel to an accumulator 16 that can beembodied, for example, in the form of a tube or in any other shape. Atleast one line 18 leads from the accumulator 16 to at least one injector20 associated with a cylinder of the engine; preferably, the accumulator16 is connected to a number of injectors 20. Each of the injectors 20 isprovided with an electric control valve 22 that controls at least oneopening of the respective injector in order to trigger or prevent a fuelinjection through the injector 20. An electronic control unit 23triggers the control valves 22 and, as a function of operatingparameters of the engine such as engine speed, load, temperature, etc.,determines the time and duration of the fuel injection through theinjectors 20. A fuel return for unused fuel leads back from theinjectors 20, for example via a line 24 that is shared by all of theinjectors 20. A line 26 functioning as a return can also lead from theaccumulator 16 back to the fuel tank 10, which line contains apressure-limiting valve or pressure control valve 28 that prevents animpermissibly high pressure from building up in the accumulator 16 andcan vary the pressure prevailing in the accumulator 16. Between theaccumulator 16 and the injectors 20, a pressure boosting device 21 canbe provided, which further increases the pressure available for fuelinjection in comparison to the pressure prevailing in the accumulator16. The pressure boosting device 21 is preferably integrated into theinjector 20 and is embodied in the form of a hydraulic pressure booster.In this case, the fuel return 24 preferably leads from the pressurebooster 21 of the injectors 20.

The high-pressure pump 14 is mechanically driven by the internalcombustion engine and is therefore driven in proportion to the speed ofthe engine. In a first exemplary embodiment shown in FIG. 1, the fuelsupply pump 12 is likewise mechanically driven by the engine or thehigh-pressure pump 14. In this case, the fuel supply pump 12 ispreferably mounted onto the high-pressure pump 14 or integrated into it.A filter 30 is provided between the fuel supply pump 12 and the fueltank 10. In addition, a throttle restriction 31 can be provided in theconnection between the fuel supply pump 12 and the fuel tank 10 in orderto limit the flow. The fuel tank 10 can contain a collecting reservoir32 from which the fuel supply pump 12 draws fuel and into which a jetpump 33 delivers fuel from the fuel tank 10. The motive flow of the jetpump 33 is supplied to it from the accumulator 16 via the fuel return26.

The high-pressure pump 14 can be embodied in the form of a radial pistonpump and has at least one and possibly several pump elements, each ofwhich has a pump piston that delimits a pump working chamber and isdriven into a reciprocating motion by drive shaft. A fuel metering unit36 is provided between the fuel supply pump 12 and the high-pressurepump 14. The fuel metering unit 36 has a control valve 38 that isactuated, for example, by an electric actuator 37, preferably anelectromagnet or a piezoelectric actuator, and can continuously adjustthe flow from the fuel supply pump 12 to the high-pressure pump 14. Thecontrol valve 38 can be embodied in the form of a proportional valvethat can continuously change the flow cross section between the fuelsupply pump 12 and high-pressure pump 14. Alternatively, the controlvalve 38 can also be opened and closed cyclically, which makes itpossible to change an average effective flow cross section between thefuel supply pump 12 and the high-pressure pump 14. The fuel meteringunit 36 is preferably mounted onto the high-pressure pump 14 orintegrated into it, but can also be disposed separate from thehigh-pressure pump 14. The control unit 23 triggers the fuel meteringunit 36 in such a way that the fuel supply pump 12 delivers a fuelquantity to the high-pressure pump 14 that the high-pressure pump 14then in turn delivers at high pressure to the accumulator 16 in order tomaintain a predetermined pressure in the accumulator 16 as a function ofoperating parameters of the internal combustion engine. The accumulator16 is associated with a pressure sensor in the pressure control valvethat is connected to the control unit 23 and supplies it with a signalindicating the current pressure in the accumulator 16.

The fuel return 24 from the injectors 20 feeds into the connectionbetween the fuel supply pump 12 and the fuel metering unit 36. Aconnection 40 controlled by a pressure valve 42 leads from the fuelreturn 24 to a discharge region that can be comprised, for example, ofthe fuel tank 10. The pressure valve 42 opens the connection 40 when apredetermined pressure is exceeded so that fuel can flow out into thefuel tank 10. The connection 40 can feed into the return line 26 fromthe accumulator 16 so that the fuel quantity diverted via the pressurevalve 42 is also supplied to the jet pump 33 as a motive flow. Thepressure valve 42 is preferably mounted onto the high-pressure pump 14or integrated into it. The connection 40 branches off from the fuelreturn 24 spaced apart from its outlet into the connection between thefuel supply pump 12 and the fuel metering unit 36, thus yielding a fuelreturn segment 24 a that extends between the outlet and thebranching-off point of the connection 40.

From the connection between the fuel supply pump 12 and the fuelmetering unit 36, in a region between the fuel supply pump 12 and theoutlet of the fuel return segment 24 a, a bypass connection 44 branchesoff to a drive region of the high-pressure pump 14. The drive region ofthe high-pressure pump 14 referred to here includes its drive shaft aswell as the region in which the rotary motion of the drive shaft isconverted into the reciprocating motion of the pump pistons. The fuelflowing via the bypass line 44 into the drive region assures alubrication and cooling of the drive region. The bypass connection 44preferably contains a throttle restriction 45 to limit the fuel quantitysupplied to the drive region. A return 46 leads from the drive region ofthe high-pressure pump 14 back to the fuel tank 10 and can feed, forexample, into the connection 40 and the return 26 from the accumulator16. The return 46 assures a constant flow through the drive region ofthe high-pressure pump 14.

The function of the fuel injection system according to the firstexemplary embodiment will be explained below. During operation of theinternal combustion engine, the fuel supply pump 12 draws fuel from thefuel tank 10 and delivers it via the fuel metering unit 36 to thesuction side of the high-pressure pump 14. The high-pressure pump 14delivers fuel at high pressure to the accumulator 16. The injectors 20inject fuel into the cylinders of the engine and the control unit 23determines the timing of the fuel injection and the quantity of injectedfuel by triggering the control valves 22 as a function of operatingparameters of the engine. The control unit 23 also triggers the fuelmetering unit 36 so that it sets a flow cross section great enough thatthe high-pressure pump 14 draws and delivers to the accumulator 16 thefuel quantity required to maintain a predetermined pressure in theaccumulator 16.

Particularly if the injectors 20 are provided with pressure boosters 21,depending on the operating state of the engine, the high-pressure pump14 must deliver a large quantity of fuel to the accumulator 16 and thefuel supply pump 12 must deliver this large quantity of fuel from thefuel tank 10 to the high-pressure pump 14. This can require that thefuel supply pump 12 be designed with very large dimensions. According tothe present invention, however, the fuel supply pump 12 is dimensionedso that the maximum quantity of fuel it can deliver is less than themaximum quantity of fuel that the high-pressure pump 14 must take in anddeliver to the accumulator 16. In operating states in which the quantityof fuel that the fuel supply pump 12 delivers from the fuel tank 10 isinsufficient, the high-pressure pump 14 takes in part of the fuelquantity flowing from the injectors 20 through the fuel return 24 inaddition to the quantity of fuel delivered by the fuel supply pump 12.In the process of this, part of the fuel flowing through the fuel return24 flows out through the fuel return segment 24 a into the connectionbetween the fuel supply pump 12 and the fuel metering unit 36 and istaken in by the high-pressure pump 14. The remaining part of thequantity of fuel flowing through the fuel return 24 flows through theopen pressure valve 42, via the connection 40, and into the fuel tank10. The quantity of fuel flowing into the drive region via the bypassline 44 is thus exclusively drawn from the quantity of fuel that thefuel supply pump 12 delivers from the fuel tank 10 and is thereforerelatively cool. The fuel quantity taken in by the high-pressure pump 14is likewise relatively cool since only part of this fuel quantity isdrawn from the heated fuel return 24.

In operating states in which the fuel quantity that the fuel supply pump12 delivers from the fuel tank 10 is sufficient to supply the requiredintake quantity of the high-pressure pump 14, the high-pressure pump 14only takes in fuel delivered by the fuel supply pump 12 and the entirequantity of fuel flowing through the fuel return 24 is conveyed throughthe open pressure valve 42, via the connection 40, and into the fueltank 10. In operating states in which the fuel supply pump 12 delivers aquantity of fuel greater than the required intake quantity of thehigh-pressure pump 14, part of the fuel quantity delivered by the fuelsupply pump 12 is conveyed back through the fuel return segment 24 a andthrough the open pressure valve 42, via the connection 40, and likewiseinto the fuel tank 10. In these operating states, the high-pressure pump14 consequently only takes in the relatively cool fuel quantitydelivered by the fuel supply pump 12.

The fuel flows through the fuel return segment 24 a in differentdirections depending on the operating state. If the quantity of fueldelivered by the fuel supply pump 12 is less than the required intakequantity of the high-pressure pump 14, then a partial quantity of thefuel quantity flowing back from the injectors 20 through the fuel return24 flows through the fuel return segment 24 a in the direction towardthe high-pressure pump 14. If the quantity of fuel delivered by the fuelsupply pump 12 is greater than the required intake quantity of thehigh-pressure pump 14, then a partial quantity of the fuel quantitydelivered by the fuel supply pump 12 flows through the fuel returnsegment 24 a in the direction toward the pressure valve 42. The fuelreturn segment 24 a thus assures that when the delivery quantity of thefuel supply pump 12 is sufficient, the high-pressure pump 14 only takesin fuel delivered by the fuel supply pump 12 and only when the deliveryquantity of the fuel supply pump 12 is insufficient, does thehigh-pressure pump 14 also take in fuel from the fuel return 24. Onlythe fuel quantity delivered by the fuel supply pump 12 flows through thefilter 30, whereas the fuel quantity drawn from the fuel return 24 isnot introduced until after the filter 30. But the excess fuelpotentially delivered by the fuel supply pump 12 and diverted via thefuel return segment 24 a, the pressure valve 42, and the connection 40also flows through the filter 30.

FIG. 2 shows the fuel injection system according to a second exemplaryembodiment in which the fundamental design is the same as in the firstexemplary embodiment and only the fuel supply pump 12 has been modified.The fuel supply pump 12 is disposed separate from the high-pressure pump14, has an electric drive unit, and is preferably disposed inside thefuel tank 10. The filter 30 is provided between the fuel supply pump 12and the fuel metering unit 36; the bypass connection 44 to the driveregion of the high-pressure pump 14 branches off between the filter 30and the fuel metering unit 36. Inside the fuel tank 10, a return 48 thatleads back into the fuel tank 10 and is controlled by a pressure valve49 branches off from the connection of the fuel supply pump 12 to thefilter 30. The pressure valve 49 and the return 48 limit the pressurebetween the fuel supply pump 12 and the filter 30, thus preventing animpermissible increase in pressure if the filter 30 becomes clogged, forexample. The remainder of the design and function of the fuel injectionsystem according to the second exemplary embodiment is the same as inthe first exemplary embodiment described above.

FIG. 3 shows the fuel injection system according to a third exemplaryembodiment in which the fundamental design is the same as in the secondexemplary embodiment, but the disposition of the pressure valve 42 andthe fuel return segment 24 a has been modified. The fuel supply pump 12has an electric drive unit and is disposed in the fuel tank 10. Thebypass connection 44 leading to the drive region of the high-pressurepump 14 branches off between the filter 30 and fuel metering unit 36.The fuel return 24 from the injectors 20 feeds into the connectionbetween the fuel supply pump 12 and the filter 30. The connection 40controlled by the pressure valve 42 leads from the fuel return 24 to thefuel tank 10. The fuel return segment 24 a is disposed between thebranch-off point of the connection 40 and the outlet of the fuel return24 into the connection between the fuel supply pump 12 and the filter30. In the third exemplary embodiment, the pressure valve 42 can bedisposed separate from the high-pressure pump 14.

The function of the fuel injection system according to the thirdexemplary embodiment is essentially the same as in the first and secondexemplary embodiments. Fuel flows through the fuel return segment 24 ain different directions depending on the operating state. If the fuelquantity delivered by the fuel supply pump 12 is less than the requiredintake quantity of the high-pressure pump 14, then a partial quantity ofthe fuel quantity flowing from the injectors 20 through the fuel return24 flows through the fuel return segment 24 a in the direction towardthe high-pressure pump 14. If the fuel quantity delivered by the fuelsupply pump 12 is greater than the required intake quantity of thehigh-pressure pump 14, then a partial quantity of the fuel quantitydelivered by the fuel supply pump 12 flows through the fuel returnsegment 24 a in the direction toward the pressure valve 42. The fuelreturn segment 24 a thus assuring that if the delivery quantity of thefuel supply pump 12 is sufficient, then the high-pressure pump 14exclusively takes in fuel delivered by the fuel supply pump 12 and onlyif the delivery quantity of the fuel supply pump 12 is insufficient,does the high-pressure pump 14 also take in fuel from the fuel return24. By contrast with the first and second exemplary embodiments, in thethird exemplary embodiment, the entire quantity of fuel taken in by thehigh-pressure pump 14 flows through the filter 30. The excess fuelpotentially delivered by the fuel supply pump 12, however, does not flowthrough the filter 30 because it is diverted via the fuel return segment24 a, the pressure valve 42, and the connection 40 before reaching thefilter 30. Only with a sufficient delivery quantity of the fuel supplypump 12 is the fuel quantity delivered to the drive region of thehigh-pressure pump 14 via the bypass connection 44 diverted exclusivelyfrom the cold fuel supply that the fuel supply pump 12 delivers from thefuel tank 10. When the delivery quantity of the fuel supply pump 12 isinsufficient, the fuel quantity delivered to the drive region is drawnfrom the mixture of the cold fuel that the fuel supply pump 12 deliversfrom the fuel tank 10 and the heated fuel taken from the fuel return 24.By contrast with the first and second exemplary embodiments, in thethird exemplary embodiment, when the delivery quantity of the fuelsupply pump 12 is insufficient, the drive region of the high-pressurepump 14 is consequently supplied with fuel at a slightly highertemperature.

The foregoing relates to preferred exemplary embodiments of theinvention, it being understood that other variants and embodimentsthereof are possible wherein the spirit and scope of the invention, thelatter being defined by the appended claims.

1. A fuel injection system for an internal combustion engine, the systemcomprising a high-pressure pump that delivers fuel at high pressure toan accumulator, a fuel supply pump that delivers fuel to the suctionside of the high-pressure pump, a fuel metering unit connected betweenthe fuel supply pump and the high-pressure pump and operable to variablyadjust the fuel quantity taken in by the high-pressure pump, at leastone injector connected to the accumulator for injecting fuel into theengine, a fuel return from the at least one injector, the fuel returnfrom the at least one injector feeding into the connection between thefuel supply pump and the fuel metering unit, and a connection controlledby a pressure valve leading from the fuel return to a discharge region,the high-pressure pump only drawing fuel from the fuel return inoperating states in which the fuel quantity delivered by the fuel supplypump is less than the required intake quantity of the high-pressurepump.
 2. The fuel injection system according to claim 1, wherein thehigh-pressure pump draws from the fuel return only the differencebetween its required intake quantity and the fuel quantity delivered bythe fuel supply pump.
 3. The fuel injection system according to claim 1,wherein the branch-off point of the connection leading from the fuelreturn to the discharge region is disposed spaced apart from the outletof the fuel return into the connection between the fuel supply pump andthe fuel metering unit, which spacing yields a fuel return segmentbetween the outlet of the fuel return and the branch-off point of theconnection leading to the discharge region.
 4. The fuel injection systemaccording to claim 2, wherein the branch-off point of the connectionleading from the fuel return to the discharge region is disposed spacedapart from the outlet of the fuel return into the connection between thefuel supply pump and the fuel metering unit, which spacing yields a fuelreturn segment between the outlet of the fuel return and the branch-offpoint of the connection leading to the discharge region.
 5. The fuelinjection system according to claim 1, further comprising a bypass lineto a drive region of the high-pressure pump branches off from theconnection between the fuel supply pump and the fuel metering unit. 6.The fuel injection system according to claim 2, further comprising abypass line to a drive region of the high-pressure pump branches offfrom the connection between the fuel supply pump and the fuel meteringunit.
 7. The fuel injection system according to claim 3, furthercomprising a bypass line to a drive region of the high-pressure pumpbranches off from the connection between the fuel supply pump and thefuel metering unit.
 8. The fuel injection system according to claim 4,further comprising a bypass line to a drive region of the high-pressurepump branches off from the connection between the fuel supply pump andthe fuel metering unit.
 9. The fuel injection system according to claim5, wherein between the fuel metering unit and the branch-off point ofthe bypass connection, the fuel return feeds into the connection betweenthe fuel supply pump and the fuel metering unit.
 10. The fuel injectionsystem according to claim 6, wherein between the fuel metering unit andthe branch-off point of the bypass connection, the fuel return feedsinto the connection between the fuel supply pump and the fuel meteringunit.
 11. The fuel injection system according to claim 7, whereinbetween the fuel metering unit and the branch-off point of the bypassconnection, the fuel return feeds into the connection between the fuelsupply pump and the fuel metering unit.
 12. The fuel injection systemaccording to claim 5, wherein between the fuel supply pump and thebranch-off point of the bypass line, the fuel return feeds into theconnection between the fuel supply pump and the fuel metering unit. 13.The fuel injection system according to claim 6, wherein between the fuelsupply pump and the branch-off point of the bypass line, the fuel returnfeeds into the connection between the fuel supply pump and the fuelmetering unit.
 14. The fuel injection system according to claim 7,wherein between the fuel supply pump and the branch-off point of thebypass line, the fuel return feeds into the connection between the fuelsupply pump and the fuel metering unit.
 15. The fuel injection systemaccording to claim 1, wherein the suction side of the fuel supply pumpis preceded by a filter and/or the pressure side of the fuel supply pumpis followed by a filter and, downstream of the filter, the fuel returnfeeds into the connection between the fuel supply pump and the fuelmetering unit.
 16. The fuel injection system according to claim 1,wherein the suction side of the fuel supply pump is preceded by a filterand/or the pressure side of the fuel supply pump is followed by a filterand, upstream of the filter, the fuel return feeds into the connectionbetween the fuel supply pump and the fuel metering unit.
 17. The fuelinjection system according to claim 3, wherein the suction side of thefuel supply pump is preceded by a filter and/or the pressure side of thefuel supply pump is followed by a filter and, upstream of the filter,the fuel return feeds into the connection between the fuel supply pumpand the fuel metering unit.
 18. The fuel injection system according toclaim 1, wherein the fuel supply pump has an electric drive unit. 19.The fuel injection system according to claim 1, wherein the fuel supplypump is mechanically driven by the internal combustion engine or by thehigh-pressure pump.
 20. The fuel injection system according to claim 1,wherein the at least one injector has a pressure boosting unit disposedon it, from which the fuel return leads.